1. Field of the Invention.
This invention relates generally to making a curved shadow mask having small openings or slits for use in colored television tubes as well as for other articles. More specifically, this is an etched mask and an etching process for producing a flat shadow mask with a plurality of apertures therein which can be molded or curved in the working region of the mask as well as the flange areas of the mask to produce a smooth, stress-free aperature mask.
2. Description of the Prior Art
In a colored television picture tube, a shadow mask or aperture mask is located between the electron guns at the rear of the tube and the phosphor dots on the faceplate at the face of the tube. Electron beams pass through the tiny openings or apertures of the shadow mask and impinge on a suitable color producing phosphor dot on the faceplate. Located in line with the openings of the shadow mask are three phosphor dots, lines or the like -- one dot or line for each of the primary colors. During operation of the picture tube, the shadow mask openings are used as a guide for the electron beams. In one type of these prior art masks, the openings are relatively small and elongated. The process of making openings in an elongated shape is shown and described in a co-pending application by Frantzen and Barton, entitled "Etching process for Accurately Making Small Holes in Thick Materials", Ser. No. 487,663, filed July 11, 1974.
The present invention relates to making a mask having elongated openings therein and providing the mask with a plurality of similar recessed regions to allow for two dimensional forming of the mask to produce a smooth, continuous rounded surface even in the marginal areas of the shadow mask.
Recently, the shadow mask industry has begun using the types of shadow masks which have elongated slots or slits located in vertical lines in the face of the mask. Generally, the openings in the face of the masks have a minimum dimension which is less than the thickness of the mask material. In addition, the openings are located in vertical alignment on the face of the mask. These factors coact to make it difficult to etch a shadow mask and then form the mask into a curved mask suitable for use in a television picture tube. One of the problems encountered with forming the mask is that because the sets of openings are located in vertical alignment, the mask region between the openings ruptures easily when the mask is domed or formed into the required shape for insertion into the television picture tube.
The present invention has been found to eliminate the difficulty of forming a smooth curved surface from a sheet of flat material having a set of slot-like openings located in alignment with one another and parallel to one another. Briefly, the present invention provides a set of recesses which are not interconnected but are located in a symetric pattern throughout the margin and the face of the mask, i.e., the pattern of recesses is located in the margin and edges of the mask even though the apertures or slits are not located in the margins of the mask. It has been found that the present arrangement of recess areas allows for smoothly forming or doming of the mask in both the face region of the mask and the margin area of the mask.
The co-pending application of applicant's shadow mask construction filed September 20, 1974, U.S. Ser. No. 507,689, now U.S. Pat. No. 3,916,243, shows and describes a process for preventing rupture of the tie bars on the face of a shadow mask by use of parallel grooves or channels located between the etched slots on the mask. The present invention in contrast, provides for a pattern of recesses which extend the length of the mask and are dispersed and matched with the slot openings in the mask. The pattern of recesses extend throughout both the face and the margin of the mask. With the pattern of recesses shown and described herein, it has been found that the mask can be smoothly curved and domed into the proper shape for insertion into a television picture tube.